Currently, numerous aircraft use piloting aid devices making it possible to facilitate the interpretation of data related to the aircraft, to the ground or to the environment in which the aircraft is deploying.
For example, a system commonly used in certain aircraft under the acronym HUD, standing for “Head Up Display” in aeronautical terminology, makes it possible to display flight information superimposed on the landscape seen through the windscreen of the cockpit. It makes it possible to facilitate certain critical phases of flight, notably landings.
The computation and representation of symbols, also called symbology in aeronautical terminology, presented to the pilot superimposed on the landscape is commonly used.
In order to improve the exterior view from the cockpit, when visibility conditions are poor, a sensor located in the aircraft's nose can provide an image of video type presented in the HUD. This image constitutes a piloting aid which is particularly helpful notably during an approach phase. It makes it possible to improve the interpretations of the landscape and the recognition of certain zones. It therefore constitutes an enhancement of safety in landing phases for example.
Furthermore, the video image makes it possible to delay the point from which fly by sight is considered to be necessary notably during a landing. This point is called the “point of vision” in the subsequent description. From the piloting point of view, the pilot can decide later on about a landing if the conditions so permit.
Increasing the duration for which the pilot expects to have visibility of the runway by sight makes it possible to approach close to the runway and to obtain a greater chance of having a clear field of vision in proximity to the runway, for example in the case of bad weather.
If the pilot cannot see the runway at the point of vision then he is obliged not to land under these conditions. The presence of a video image allows the pilot to push back in time, therefore to a lower altitude, the position of the point of vision in his approach procedure.
A sensor providing a video image of this type is known in aeronautics by the acronym EVS standing for “Enhanced Vision System” in aeronautical terminology.
The EVS is a camera of mono-band or multi-band infrared type having the ability to see “better” than the human eye in conditions of low brightness, typically during night flights or poor weather, such as the presence of fog or smoke.
This sensor is generally located in the aircraft's nose and has a field of vision positioned in a similar manner to that of the HUD.
This EVS system is generally coupled to the HUD for certain applications notably in the approach phase so as to improve visibility in the field of vision. It therefore makes it possible to obtain better operational minima, such as the minimum altitude at which a landing decision does or does not have to be taken.
An advantage of the image provided by the EVS is that it is of video type, that it covers the whole of the field of the HUD and that it is presented superimposed on the HUD symbology.
Although this synthetic vision, which is fairly close in terms of rendition to real vision, facilitates the perception of the exterior world in poor meteorological conditions, drawbacks remain.
Among them, the enhancement afforded by this piercing vision is counteracted by the overload of the image provided above the true landscape.
This renders the image almost unusable and may generate confusion of interpretation between the real world and the EVS imaging notably during the required identification of exterior elements in the final landing procedure. The pilot must perform a go-around if the visibility does not make it possible to identify the elements necessary for landing, such as the threshold of the landing runway for example.
Document WO00/54217 is known from the prior art. This document describes an HUD display device on which images originating from several measurement sources can be displayed separately or at the same time by merging the captured images. This document discloses a scheme for creating an improved synthetic image by virtue of contour detection processing. According to this solution, the aim of the means for generating an image is to create a more complete image than that captured or an entirely synthetic image representing the landscape background. The major disadvantage of this solution is the problem of overload of the displayed image.
The invention makes it possible to alleviate the aforesaid drawbacks.